1. Field of the Invention
The present invention relates to an apparatus for recording and reproducing optical information in which a light beam from a semiconductor laser is irradiated onto an optical information recording medium through a tracking mirror and an objective lens to perform recording, reproducing and erasing operations with respect to the optical information.
2. Description of the Related Art
An appratus for recording and reproducing various kinds of optical information has an optical pickup in a carriage for example. In such an optical pickup, a light beam from a semiconductor laser is transmitted through a coupling lens, a polarizing beam splitter, a .lambda./4 plate, etc. Thereafter, the light beam is reflected by a reflecting face of a rotatable tracking mirror and is converged by an objective lens and is then irradiated onto an optical information recording medium so as to form a small light spot. The reflected light from the optical information recording medium is again transmitted to the polarizing beam splitter through the objective lens, the tracking mirror and the 1/4 plate and is then received by a light-receiving element through a convex lens and a cylindrical lens. When a predetermined detecting signal is transmitted from in the light-receiving element, a tracking error signal is generated from a tracking error signal generating circuit and is supplied to a phase compensating circuit. A driving signal generated from the phase compensating circuit is supplied to a tracking drive motor through a drive circuit for driving the tracking drive motor, thereby adjusting the rotation of the tracking mirror. Another driving signal generated from the phase compensating circuit is supplied to a seek motor through a drive circuit for driving the seek motor so as to move the carriage.
In such an apparatus for recording and reproducing optical information, the rotary angle of the tracking mirror for reflecting and irradiating the reproduced light beam onto the optical information recording medium is adjusted and controlled to accurately scan the light beam for reproduction on a recorded trace. At a recording time, the rotary position of the tracking mirror is detected by a light beam for detection different from the light beam for record and is controlled on the basis of an output detected by this light beam for detection. Such an apparatus is shown in Japanese Utility Model publication (KOKOKU) No. 60-34100.
However, in the above controller for controlling the rotary position of the tracking mirror, the rotary position of the tracking mirror is not adjusted to suitably maintain the diameter of a small light spot irradiated onto the optical information recording medium. For example, the light beam must be incident within a range of angle 0.degree..+-.40' with respect to the objective lens to form the spot having size 1 .mu.m for example. However, there is a case in which the rotary angle of the tracking mirror exceeds a range of angle 0.degree..+-.20' by the influence of an operating state of a mechanism for attaching the tracking mirror thereto or various kinds of vibrations. In such a case, the reflected light from the tracking mirror is incident to the objective lens at an incorrect angle so that the size of the small light spot irradiated onto the optical information recording medium exceeds an allowable range thereof and the light spot is incorrectly enlarged and modified.